Why don't static objects detect collisions with other static objects?
It is that way by design - most likely for performance. See the Static Physics Object page.

Static objects in the Blender Game Engine do not automatically react to physics, including gravity and collisions. Even if hit by the force of a speeding 18-wheeler truck, it will remain unresponsive in terms of location, rotation, or deformation.
It will, however, give collision reactions. Objects will bounce off of Static Objects, and rotational inertia will transfer to objects capable of rotating (that is, Rigid Body Objects will spin in response, though Dynamic Objects will not).